The RAGE signaling pathway is involved in intestinal inflammation and represents a promising therapeutic target for Inflammatory Bowel Diseases

Dietary Advanced Glycation Endproducts and the Gastrointestinal Tract

The prevalence of inflammatory bowel diseases (IBD) is increasing in the world. The introduction of the Western diet has been suggested as a potential explanation of increased prevalence. The Western diet includes highly processed food products, and often include thermal treatment. During thermal treatment, the Maillard reaction can occur, leading to the formation of dietary advanced glycation endproducts (dAGEs). In this review, different biological effects of dAGEs are discussed, including their digestion, absorption, formation, and degradation in the gastrointestinal tract, with an emphasis on their pro-inflammatory effects. In addition, potential mechanisms in the inflammatory effects of dAGEs are discussed. This review also specifically elaborates on the involvement of the effects of dAGEs in IBD and focuses on evidence regarding the involvement of dAGEs in the symptoms of IBD. Finally, knowledge gaps that still need to be filled are identified.

Association between serum soluble receptor for advanced glycation end-products (RAGE) deficiency and severity of clinicopathologic evidence of canine chronic inflammatory enteropathy

Innate immunity plays a central role in the pathogenesis of chronic inflammatory enteropathies (CIE) in dogs, and further evaluation of the innate immune receptor for advanced glycation end-products (RAGE) is warranted. We measured serum concentrations of decoy receptor soluble RAGE (sRAGE) in 102 dogs diagnosed with CIE, and evaluated relationships with clinical disease severity, histologic lesion severity, concentrations of serum C-reactive protein (CRP), and serum and fecal calprotectin, S100A12, and alpha₁-proteinase inhibitor (α₁PI). Serum sRAGE levels were not associated with clinical disease activity, serum CRP, serum and fecal α₁PI, calprotectin, or S100A12 concentrations. Microscopic lesions in the duodenum were more severe in dogs with serum sRAGE concentration ≤ 340 ng/L (p = 0.013). Serum sRAGE levels were weakly and inversely correlated with the severity of lymphoplasmacytic infiltration in the gastric antrum and duodenum, and with crypt dilation and the neutrophilic infiltrate in the duodenum, in univariate analysis (all p < 0.05), but none of the correlations remained statistically significant after correction for multiple comparisons. Our study confirms that CIE in dogs is associated with decreased serum sRAGE concentrations, suggesting a dysregulated sRAGE/RAGE axis.

An integrated metabolism in vivo analysis and network pharmacology in UC rats reveal anti-ulcerative colitis effects from Sophora flavescens EtOAc extract

Ulcerative colitis (UC), an immune system disease, is characterized by long duration and easy relapse. Sophora flavescens (S. flavescens), also named "Kushen", is a traditional Chinese medicine, widely used to treat UC in clinics. Alkaloids and flavonoids are the main constituents of S. flavescens. Previous studies indicated that the effects of S. flavescens against UC mainly attribute to its alkaloids. In view of the clinical applications of its flavonoids and our preliminary experiments on the effects of S. flavescens treatment, we speculated that flavonoids also could exert an anti-UC effect, but its efficacy and mechanism are still not yet to be revealed. Herein, we examined the pharmacodynamic effects of the ethyl acetate (EtOAc) extract of S. flavescens EtOAc (SFE) against dextran sodium sulfate-induced UC rats for the first time. Pharmacodynamic effects indicated that SFE could significantly alleviate the loss in the body weight and shortening of the colon length, reduce colon bleeding and improve colon tissue damage of UC rats. A total of 28 prototypes and 41 metabolites were unambiguously or tentatively detected in rat's plasma and urine. Among them, 28 prototypes and 3 phase I metabolites shared 40 UC targets, the targets contributed to 51 metabolic pathways in 5 modules. Additionally, genistein, formononetin, isokurarinone, kurarinone, maackiain, kushenol N, trifolirnizin, kuraridin and norkurarinone were suggested to be potential active compounds in SFE for treating UC by comprehensively investigating the results of network pharmacology analysis, metabolic analysis in vivo, and previous researches. Finally, a combination of metabolic analysis in vivo with network pharmacology can elucidate the material basis and pharmacodynamic effect of traditional Chinese medicines, and lay the foundation for further clarify the anti-UC mechanism of SFE.

Differential Expression of Soluble Receptor for Advanced Glycation End-products in Mice Susceptible or Resistant to Chronic Colitis

BACKGROUND

Identifying the factors that contribute to chronicity in inflamed colitic tissue is not trivial. However, in mouse models of colitis, we can investigate at preclinical timepoints. We sought to validate murine Trichuris muris infection as a model for identification of factors that promote development of chronic colitis.

METHODS

We compared preclinical changes in mice with a resolving immune response to T. muris (resistant) vs mice that fail to expel the worms and develop chronic colitis (susceptible). Findings were then validated in healthy controls and patients with suspected or confirmed IBD.

RESULTS

The receptor for advanced glycation end products (RAGE) was highly dysregulated between resistant and susceptible mice before the onset of any pathological signs. Increased soluble RAGE (sRAGE) in the serum and feces of resistant mice correlated with reduced colitis scores. Mouse model findings were validated in a preliminary clinical study: fecal sRAGE was differentially expressed in patients with active IBD compared with IBD in remission, patients with IBD excluded, or healthy controls.

CONCLUSIONS

Preclinical changes in mouse models can identify early pathways in the development of chronic inflammation that human studies cannot. We identified the decoy receptor sRAGE as a potential mechanism for protection against chronic inflammation in colitis in mice and humans. We propose that the RAGE pathway is clinically relevant in the onset of chronic colitis and that further study of sRAGE in IBD may provide a novel diagnostic and therapeutic target.

Analysis of Oxidative Stress-Related Markers in Crohn's Disease Patients at Surgery and Correlations with Clinical Findings

Crohn' disease (CD) patients are at high risk of postoperative recurrence and new tools for the assessment of disease activity are needed to prevent long-term complications. In these patients, the over-production of ROS generated by inflamed bowel tissue and inflammatory cells activates a pathogenic cascade that further exacerbates inflammation and leads to increased oxidative damage to DNA, proteins, and lipids. We measured the products of protein/lipid oxidation and the total antioxidant capacity (ferric reducing ability of plasma, FRAP) in the serum of CD patients with severe disease activity requiring surgery with the aim to characterize their redox status and identify associations between oxidative stress-related markers and their clinical characteristics. At the systemic level, CD was associated with increased levels of protein and lipid oxidation products when compared to healthy volunteers, even though the FRAP values were similar. Advanced oxidation protein product (AOPP) levels showed the highest difference between patients and the controls (11.25, 5.02-15.15, vs. 1.36, 0.75-2.70, median, interquartile range; p < 0.0001) and the analysis of receiver operating characteristic (ROC) curves, indicated for AOPP, the best area under the curve (AUC) value for CD prediction. Advanced glycated end-products (AGEs) were also significantly higher in CD patients (p < 0.01), which is of interest since AOPP and AGEs are both able to activate the membrane receptor for advanced glycation end products (RAGE) involved in inflammatory diseases. Thiobarbituric acid reactive substance (TBARS) levels were significantly higher in CD patients with ileal localization and aggressive disease behavior, in smokers, and in patients suffering from allergies. In conclusion, our data indicate that circulating oxidative stress biomarkers may be attractive candidates as disease predictors as well as for clinical or therapeutic monitoring of CD. Our results also suggest that AOPP/AGEs and RAGE signaling may represent a pathogenic factor and a potential therapeutic target in CD.

Role of Apple Phytochemicals, Phloretin and Phloridzin, in Modulating Processes Related to Intestinal Inflammation

Plant-derived food consumption has gained attention as potential intervention for the improvement of intestinal inflammatory diseases. Apple consumption has been shown to be effective at ameliorating intestinal inflammation symptoms. These beneficial effects have been related to (poly)phenols, including phloretin (Phlor) and its glycoside named phloridzin (Phldz). To deepen the modulatory effects of these molecules we studied: i) their influence on the synthesis of proinflammatory molecules (PGE2, IL-8, IL-6, MCP-1, and ICAM-1) in IL-1β-treated myofibroblasts of the colon CCD-18Co cell line, and ii) the inhibitory potential of the formation of advanced glycation end products (AGEs). The results showed that Phlor (10-50 μM) decreased the synthesis of PGE2 and IL-8 and the formation of AGEs by different mechanisms. It is concluded that Phlor and Phldz, compounds found exclusively in apples, are positively associated with potential beneficial effects of apple consumption.

The receptor for advanced glycation end-products (RAGE) is an important pattern recognition receptor (PRR) for inflammaging

The receptor for advanced glycation end-products (RAGE) was initially characterized and named for its ability to bind to advanced glycation end-products (AGEs) that form upon the irreversible and non-enzymatic interaction between nucleophiles, such as lysine, and carbonyl compounds, such as reducing sugars. The concentrations of AGEs are known to increase in conditions such as diabetes, as well as during ageing. However, it is now widely accepted that RAGE binds with numerous ligands, many of which can be defined as pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). The interaction between RAGE and its ligands mainly results in a pro-inflammatory response, and can lead to stress events often favouring mitochondrial dysfunction or cellular senescence. Thus, RAGE should be considered as a pattern recognition receptor (PRR), similar to those that regulate innate immunity. Innate immunity itself plays a central role in inflammaging, the chronic low-grade and sterile inflammation that increases with age and is a potentially important contributory factor in ageing. Consequently, and in addition to the age-related accumulation of PAMPs and DAMPs and increases in pro-inflammatory cytokines from senescent cells and damaged cells, PRRs are therefore important in inflammaging. We suggest here that, through its interconnection with immunity, senescence, mitochondrial dysfunction and inflammasome activation, RAGE is a key contributor to inflammaging and that the pro-longevity effects seen upon blocking RAGE, or upon its deletion, are thus the result of reduced inflammaging.